- ―Aliens' message to Destiny, transmitted in English[src]
Their average height seems to be comparable to humans. They are bipedal, like humans, but with digitigrade locomotion. They also have a pair of fish-like barbels on either side of their heads, beneath their eyes; the index digits on their hands also appear longer than the others with a claw-like feature. Their eyes seem to glow or reflect large amounts of light. Physically, they appear to be somewhat weaker than humans, as Dr. Nicholas Rush was able to overpower and strangle one without much effort. They communicate with each other in clicks and screeches, but it appears their vocal cords are either weak or non-existent as Young was unable to speak to Rush with any kind of tonal language when he was in his Nakai host. Based on their appearance and the ubiquity of water on their vessel, they may be an aquatic (or at least an amphibious) species. The atmosphere on their ships is comfortable for humans, so they are also clearly capable of breathing oxygen. (SGU: "Space")
The Nakai possess spacecraft including fighters and intergalactic motherships. They also possess technology that allows them to probe the minds of others. The device allows them to quickly learn basic information and understand the language of the probed being. It is likely they learned some English from Dr. Nicholas Rush, allowing them to transmit messages in English, though they are apparently unable to speak it themselves. They keep prisoners restrained in water-filled tanks.
They have also managed to collect some Ancient technology, as when Rush reads the mind of one of the creatures, he observes it handling a Long-range communication stone. Colonel Everett Young suspects that Rush stole this stone from the communication device box when he first found it, and the aliens confiscated it from him upon his capture. Rush neither confirms nor denies this. (SGU: "Justice", "Space", "Divided")
Nakai motherships use a form of intergalactic hyperdrive apparently extremely different to that used by any other species or culture. It is thought that these vessels are slower than those using FTL engines or Asgard hyperdrives, taking three weeks to reach a point between two of the galaxies visited by Destiny.
The aliens have known about Destiny's existence for some time and the ship has become something of an obsession to them. According to Dr. Nicholas Rush, after prolonged neural connection with one of the aliens he learned that at least one of their fighters was docked with Destiny prior to the arrival of the expedition. One fighter remained attached and transmitted a tracking signal while another fighter was seen disembarking shortly after the expedition returned from the desert planet; the former was discovered and destroyed by manually searching Destiny's hull. (SGU: "Air, Part 3", "Space", "Divided")
The expedition's first known encounter with the alien species occurred when Rush unwittingly activated the distress beacon of a crashed fighter on a Gravel pit planet. They captured Rush and suspended him in one of their holding tanks. Their existence was made known to the rest of the expedition a short time later, when Colonel Everett Young attempted to use the Long-range communication device to contact Earth and was instead connected to one of the aliens. The ship was soon thereafter attacked by their mothership. Chloe Armstrong was kidnapped in the ensuing conflict. (SGU: "Space")
Young used the communication device again to mount a rescue, unintentionally finding Rush instead. The link was severed when Rush showed Young how to use the mind probe technology. Young ordered Eli Wallace to destroy the mothership after returning to his body, while Rush rescued Chloe himself and escaped. Though Destiny does not seem to visibly damage the mothership, and was in fact close to destroying itself in the attempt, the mothership retreated shortly after Chloe and Rush escaped in a fighter. (SGU: "Space")
The Nakai later returned, having tracked Destiny using a Tracking implant implanted in Rush' chest. They arrived in three motherships and attempted to overwhelm the shields with massed fire. Rush managed to divert power to the shields, resisting the assault, while the transmitter was removed from his body and destroyed. Destiny escaped to FTL only slightly damaged. (SGU: "Divided")
When Lt. Vanessa James forgot to clear her imprint from a Long-range communication stone, the Nakai were able to use the stone in their possession to take over her body and sabotage Destiny's Faster-Than-Light engine in preparation for another attack. In addition, they placed fighters on the only Stargate within range of Destiny, trapping the crew. Two motherships mounted an attack, attempting to board the ship. Thanks to the efforts of Dr. Jeremy Franklin, the FTL drive was repaired and the ship escaped before it could be boarded. Ironically, the alien's sabotage attempt actually solved Destiny's problem of not having enough power to reach the next galaxy. (SGU: "Sabotage")
Later on, the crew discovered that Chloe was under the influence of some kind of pathogen given to her by the Nakai. Working on a cellular level, it affected her mind, causing her to go into trances where she acted strangely. She was unconsciously able to understand the Nakai language, and apparently the Ancient language as well, even when not being controlled by the pathogen. Her intellect has also increased, enabling her to solve complex equations in mere moments. Rush attempted to cure Chloe using the Destiny interface chair, however this attempt failed. Rather than tell everyone this, he made a deal with her to keep her condition quiet in exchange for her help in solving his problems. (SGU: "Pathogen")
Weeks later, Destiny began creating simulations of Destiny being attacked and destroyed by the aliens and used them to influence Young's dreams. By this time the pathogen in Chloe's blood stream had also begun to manipulate her appearance, causing grey plant-like growths to form on her skin. (SGU: "Trial and Error")
After some time, the Nakai were able to catch up to Destiny in the next galaxy. They knew where Destiny was because Chloe sent a signal out to them, as she knew they been looking for Destiny in the galaxy. Soon after this, three Nakai ships arrived, some of the Berzerker drones that Destiny was fighting went after them. While Destiny destroyed the Control Ship, two of the Nakai ships had already been destroyed and the other severely damaged. When the shuttle from Destiny tried to get a drone to study, the damaged ship blocked their way back to the ship, and transmitted the message "No Escape" in English. Destiny made a deal with them in order to get them back on the ship to study the drone, in exchange for handing Chloe over to them. The aliens agreed and removed the pathogen from her body, allowing Chloe and Lt. Matthew Scott to leave before jumping to Hyperspace. Chloe still possessed some of the abilities the pathogen gave her, such as her intellect. Chloe was sure that whatever they got from her, the Nakai will be more determined than ever to capture Destiny. (SGU: "Deliverance")
Behind the Scenes
Before the Nakai's name was revealed, viewers referred to them as blue-berry aliens.
According to Joseph Mallozzi's blog, the Nakai had been aware of Destiny for some time though it was not likely they knew of the ship's mission. However, they would have been impressed by its offensive and defensive capabilities. He suggested that they had encountered Destiny during one of its refueling stops and attempted to communicate but after receiving no response they decided to scan the ship. As time went on, their interest led them to determine the ship was unmanned and they attempted to board Destiny but were repelled by the vessel's automated defenses.
When queried on the species real name, Mallozzi refers to them as the "Nakai". Translated from Japanese to English it means "Waitress". It also translates from the Apachean group of Native American languages, meaning "from Mexico".